1. Field of the Invention
The present invention relates to the field of linear actuators for use in magnetic disk storage systems.
2. Statement of the Problem
The performance of magnetic disk drives is limited by actuator access time and actuator contention as well as by other factors. Actuator access time is the amount of time required for an actuator carrying a read/write head to move to proper position on a disk. This is constrained by the acceleration of the actuator, the mass of the actuator, friction between the actuator and its surrounding structure, the power capability of the actuator, and the distance the actuator must travel.
Actuator contention is dependent upon the availability of a particular actuator to access a particular random disk track.
Typically, read/write heads in disk drives are mounted on an arm supported by a carriage which is reciprocated by voice coil motor. The actuators usually comprise a movable carriage which is driven by an electric coil positioned in a magnetic field and operated by variable intensity and variable polarity current. This system requires considerable power to overcome the inertia of the relatively high mass of the carriage as well as inefficiencies of the linear motor. Further, these systems normally encounter friction in moving the actuator.
These actuators typically use a single actuator to move multiple read/write heads into position. This requires movement of a relatively large mass, as well as creating a problem with actuator contention. There have been various attempts to address these problems in the past.
U.S. Pat. No. 4,331,990, issued to Frandsen, discloses the use of a plurality of actuators. Each actuator has a flat wire loop mounted on top of a planar carriage frame which is mounted on roller bearings to reduce the mass and the inefficiencies of the voice oil motor system. This system still requires considerable spacing between the carriages, thus increasing the overall size and mass of the system, as well as contributing to inefficiencies in the magnetic flux. Roller bearings support the carriages which further adds mass and friction in the system.
U.S. Pat. No. 4,506,307, issued to Watrous, discloses an actuator using air bearings on portions of eight of the surfaces of an X-shaped structure of the actuator to reduce the mass of the system. The air bearings must be externally supplied by a blower.
U.S. Pat. No. 4,620,253, issued to Garwin et al., discloses an actuator using flat linear coils mounted on top of the carriage to reduce the size and mass of the carriage to increase the performance of the system.
There presently exists a need for an actuator having a rapid access time as well as reducing the overall size of the system and solving the problem of actuator contention.
3. Solution of the Problem
The present invention solves these and other problems by providing a high performance disk drive having a plurality of single arm actuators.
The present invention provides a low mass, low profile actuator having a high efficiency and extremely low friction.
The present invention provides a system where multiple actuators may easily be stacked at the normal disk spacing with as many carriages as desired.